This invention relates generally to vibratory environments, and more particularly, to methods and apparatus for resonance frequency response attenuation.
Resonance frequency activity of cables is determined by the mass and stiffness of the cable and cable/clamp support system. Resonance frequency response activity, of cables in phase and amplitude with engine imbalance forces, is dependent on phase and amplitude of the forcing function and may lead to early failure if the forcing function coincides with the modal response of the cables. Electrical conductors and cables, as installed on engines, require effective damping and support constraint to survive the high level vibratory environment in these applications.
Electrical cables are bundled and shrouded with flexible conduits allowing routing to accommodate pre-existing cable clamp/bracket locations, and have low bending rigidity. The damping characteristics must be effective over broadband frequency and thermal ranges to control mechanically induced vibratory excitation. Electrical cable routing configurations are generally tuned to be quiescent by application specific means and the vibration stability of each application is verified individually by testing, monitoring and trending. The free span clamp lengths are defined to control vibration frequency response acceptable levels. Solutions to these issues require extensive data characterization, are reactive in nature and require extensive resources to resolve.
Electrical cables and cable-like sensors, such as TNACs, are made of an inner conducting wire and an outer protective jacket. The TNAC outer protective jacket is made of Nickel-200 and flexes repeatedly due to vibratory excitation of a gas turbine engine. As the outer protective jacket repeatedly flexes, it work-hardens, becomes brittle and breaks. When the Nickel-200 outer jacket breaks the inner sensor wire is directly exposed to the harsh operating environment of the gas turbine engine and is quickly damaged.
Gas turbine engine components like the TNAC are required to satisfy on-wing life expectancy requirements by functioning for up to fifty thousand operating hours without failure. However, the average on-wing life for the TNAC is only three thousand operating hours. Consequently, the TNAC fails to meet on-wing life expectancy requirements. To avoid damaging the entire sensor and at the same time satisfy on-wing expectancy requirements, the inner sensor wire must be immobilized and protected from the outside environment. The environment includes the vibratory and temperature conditions of the engine and other miscellaneous loads such as tools hung on the outer protective jacket by maintenance workers.
Consequently, there is needed an improved damping system effective over a wide range of frequencies and applications specific to a temperature range that attenuates all vibratory activity without the need to tune to a specific frequency.